Medical handpieces having a cutting tool that is rotatably driven by power from a drive source, such as a motor, to cut a treatment site, is disclosed, for example, in JP-2004-97790-A.
The medical handpiece disclosed in this publication has a cutting tool which has a bur provided at the tip of a flexible shank, and is inserted and placed in a tubular casing. The cutting tool is detachably held in a handpiece body, and rotatably driven by power transmitted from a drive source. Between the casing and the shank is disposed a tubular intervening member. This medical handpiece is designed such that the casing, the intervening member, and the cutting tool may be flexed for a predetermined angular range, where the intervening member prevents the shank from contacting the inner surface of the casing in the curved portion.
Further, there is disclosed in JP-2005-328971-A a medical handpiece wherein inner and outer intervening members are arranged one in another between a plurality of bearings for inhibiting shaking and deterioration of durability by friction heat, which are caused by contact between the shank and the intervening members.
In the prior art medical handpiece discussed above, the deterioration of durability by friction heat generated by the contact between the shank and the inner intervening member could be inhibited. However, when the casing is flexed for a relatively large angle from its axis, the inner intervening member is pressed by the outer intervening member to be brought into contact with the shank, which is loaded accordingly. It is found that this causes new problems to be solved, i.e., rattling, increased shaking during rotation, and deterioration of operationality of the medical handpiece.